#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
using namespace std;
double a[50];
int main()
{
	int n;
	scanf("%d", &n);
	a[1] = 1;
	a[2] = 1;
	for (int i = 3; i <= n; i++)
		a[i] = a[i - 1] + a[i - 2];
	printf("%.2lf\n", a[n]);
	return 0;
}